When transporting cars, brought about are the inconveniences that the coating layers of car bodies and parts become lusterless, discolored and damaged due to suspended matters such as dirts and dusts, rain, grass pollen and the like, colliding matters such as sands and the like and contact by workers. In order to prevent such inconveniences, wax-based materials are applied on the coating layers of car bodies and parts of automobiles, or protective sheets are adhered thereon.
However, in heating and curing coating layers applied on car bodies and parts, the curing reaction of the coating layers does not sufficiently proceed in a certain case even after passing through a drying furnace.
Among them, in the case of a bumper which is one of parts for automobiles, synthetic resin-made bumpers have come to be used in place of conventional metal-made ones in order to reduce a weight thereof, and the above synthetic resin-made bumpers are usually coated in order to improve its appearance. In the case of the above synthetic resin-made bumpers, protective sheets are adhered thereon as well in order to prevent the inconveniences described above.
However, in heating and curing coating layers applied on synthetic resin-made bumpers, the curing temperature can not be elevated in order to avoid adverse affections such as deterioration and deformation of the resin. Accordingly, the coating layers on the coated resin-made bumpers are insufficiently dried even after passing through a drying furnace, and therefore a small amount of the solvent remains or the curing reaction does not sufficiently proceed in a certain case.
When adhering a protective sheet on a coating layer in such state, brought about are problems such as “stepping (the phenomenon that deformations brought about by fine wrinkles and lifting produced on the sheet in adhering the protective sheet are transferred onto the coating layer, whereby the coating layer is deformed)”, “whitening (the phenomenon that deviation is caused in the composition of the coating layer due to affinity thereof with a pressure-sensitive adhesive layer of the sheet and that the coating layer looks white when stripping the sheet)” and “adhesive deposit (the phenomenon that the pressure-sensitive adhesive layer is partially transferred onto the coating layer when stripping the sheet)”.
Proposed as a protective sheet for a coating layer are a sheet prepared by providing a layer of a polyisobutylene-based pressure-sensitive adhesive on a substrate for supporting (for example, a Patent Document 1), a sheet prepared by providing a layer of a pressure-sensitive adhesive comprising butyl rubber or a styrene-ethylene.butylene-styrene block copolymer on a substrate for supporting (for example, a Patent Document 2), a sheet prepared by providing a layer of a composition obtained by mixing a polyisobutylene-based pressure-sensitive adhesive with a small amount of an acrylic-based pressure-sensitive adhesive on a substrate for supporting (for example, a Patent Document 3), a sheet prepared by providing a layer of a composition obtained by blending an acrylic-based pressure-sensitive adhesive with a multifunctional isocyanate compound on a substrate for supporting (for example, a Patent Document 4), a sheet prepared by providing an ethylene-vinyl acetate-glycidyl methacrylate copolymer on a substrate for supporting (for example, a Patent Document 5) and a sheet prepared by providing a pressure-sensitive adhesive layer obtained by photo-curing a resin comprising a principal component of an ionomer obtained by subjecting an ethylene-methacrylic acid copolymer to intermolecular bonding with metal ions on a substrate for supporting (for example, a Patent Document 6).
However, the performances of the protective sheets for a coating layer which have the pressure-sensitive adhesive layers described above are not still satisfactory.    Patent Document 1: U.S. Pat. No. 2,701,020    Patent Document 2: U.S. Pat. No. 3,668,322    Patent Document 3: U.S. Pat. No. 2,832,565    Patent Document 4: U.S. Pat. No. 3,342,977    Patent Document 5: JP 1998-121002A    Patent Document 6: JP 1998-121010A